Forming apparatus



y 1967 J. J. ASTLEFORD, JR 3,318,127

FORMING APPARATUS Filed Aug. 24, 1964 3 Sheets-Sheet 1 FIG. I. 1 FIG. 2. I4 IO PRIOR ART 20 I2 1 l8 l2 DIRECT CURRENT L1] POWER T SUPPLY PRIOR ART FIG. 3A.

WITNESSES 0% Z%( I do n J. As ford, Jr. 4 04 J OIB/IQQJ INVENTOR May 9, 196 J. J. ASTLEFORD, JR

FORMING APPARATUS 3 Sheets-Sheet 2 Filed Aug. 24, 1964 y 1967 J. J. ASTLEFORD, JR 3,318,127

FORMING APPARATUS 5 Sheets-Sheet 5 Filed Aug. 24, 1964 N wE 5&3 529.

United States Patent 3,318,127 FORMING APPARATUS John J. Astleford, Jr., Sharon, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 24, 1964, Ser. No. 391,597 8 Claims. (Cl. 72-56) This invention relates in general to the magnetic shaping or forming of metals and more particularly to apparatus for performing magnetic shaping of metals.

In the magnetic forming of metal, a very short electrical current pulse or pulse of electrical energy, such as from a charged capacitor bank, is applied to an electromagnetic coil. The electromagnetic coil produces a high intensity magnetic field and induces high currents into a closely coupled workpiece or part to be formed, with the magnetic field produced by the induced currents in the workpiece interacting with the magnetic field of the electromagnetic coil to produce a mechanical force on the workpiece. The quantity of electrical energy and duration of the pulse are predetermined to give the desired forming action.

In order to utilize one basic size of electromagnetic coil for a variety of workpiece sizes and shapes, or to concentrate the magnetic field, or to direct the magnetic field into areas which may not be readily accessible to the relatively large and bulky electromagnetic coil, or for a combination of these or other reasons, a flux concentrator or field shaper is often inserted between the electromagnetic coil and the workpiece. Field shapers have been widely used in the induction heating of metals, with a paper by Babat and Losinsky in the Journal of Applied Physics, vol. 11, pages 816823, December 1940, describing an early use of a flux concentrator in the induction heating of metals. These flux concentrators or field shapers of the prior art are usually constructed of a good electro-conducting metal, such as copper, and are machined to allow close inductive coupling with the electromagnetic coil. The workpiece is positioned within an axially extending aperture or central opening machined in the field shaper. The wall of the field shaper has a radial slot extending completely through the wall to prevent the field shaper from acting as a short circuited turn magnetically coupled to the electromagnetic coil, which would absorb substantially all of the energy from the electromagnetic coil. The induced currents or eddy currents produced in the field shaper, screen or shield the internal metal of the field shaper from the magnetic field produced by the electromagnetic coil, causing the magnetic field of the electromagnetic coil which would ordinarily pass through the volume occupied by the field shaper, to be squeezed or concentrated into the opening between the electromagnetic coil and field shaper, and more importantly into the central opening of the field shaper where the workpiece is located. Thus, the magnetic field from the electromagnetic coil is highly concentrated in the central opening or workpiece area of the field shaper.

The radial slot extending through the wall of the field shaper, necessary to prevent the field shaper from acting as a short circuited turn, however, produces disadvantages when applied to magnetic formin applications. Magnetic forming is accomplished with short pulses of predetermined quantities of electrical energy, whose duration is in the order of 20 microseconds. Thus, any distortion in the magnetic field is reflected into the workpiece. In induction heating, which has a relatively long heating time compared to the pulse times of magnetic forming, distortions in the magnetic field are not as serious, as the heat flow in the workpiece makes minor irregularities unnoticeable, and the workpiece may be rotated to subject all of the surface to be heated to the same average magnetic field. In magnetic forming, these methods of equalizing the effect of distorted or unequal magnetic fields are not suitable. Thus, when the magnetic field from the electromagentic coil is being squeezed into the aperture or axial opening in the field shaper, a portion of the magnetic field also leaks into the slot in the field shaper, changing the direction of the magnetic field and the resulting directing of the mechanical force in this area. More specifically, the radial slot in the field shaper, being parallel with the axis of the field shaper and thus parallel with the magnetic field, presents a path of lower reluctance to the magnetic field than the path through the opening in the field shaper, resulting in a considerable leakage of the magnetic field. This leakage of the magnetic field results in a change in direction of the mechanical forces in the vicinity of the slot and results in a reduction of the mechanical force applied to the workpiece adjacent the slot. Thus, an undesirable bu-mp or raised portion occurs in this area of the workpiece.

Accordingly, it is an object of this invention to provide new and improved apparatus for magnetic forming.

Another object of this invention is to provide new and improved magnetic forming apparatus which subjects the workpiece to a uniform magnetic field.

A further object of this invention is to provide new and improved magnetic forming apparatus which utilizes a field shaper and provides a uniform magnetic field free of any disturbances due to the field shaper.

Still another object of the invention is to provide a new and improved field shaper for magnetic forming of metals.

Another object of the invention is to provide a new and improved field shaper for magnetic forming of metals which provides a uniform magnetic field.

Briefly, the present invention accomplishes the above cited objects by providing magnetic forming apparatus in which the field shaper does not have the axially extending radial slot required by field shapers of the prior art. Thus, the magnetic field and resulting mechanical forces on the workpiece are uniform, resulting in uniformity in the forming operation.

More specifically, instead of the conventional single turn field shaper with its axially extending radial slot, a field shaper having a plurality of turns is provided, in which the starting and finishing turns are not connected to each other. Since the starting and finishing turns are not connected, but are allowed to float, the field shaper meets the requirement of not providing a short-circuit turn or. turns, which would absorb all of the energy from the electromagnetic coil, and still does not have the axial radial slot which disturbs the magnetic field in its vicinity. The plurality of turns of the field shaper may be shaped as required to direct the magnetic field into the desired area and to concentrate the magnetic field, and it provides a uniform magnetic field for the uniform forming of the workpiece.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which:

FIGURE 1 is a schematic diagram of a typical metal forming circuit;

FIG. 2 is a side elevation, partially in section and partially schematic, of typical prior art metal forming apparatus, including an electromagnetic coil, field shaper and workpiece;

FIG. 2A is a top view of the field shaper shown in FIG. 2;

FIG. 3 is a side elevation, partially in section and partially schematic, of metal forming apparatus illustrating an embodiment of the invention, including an electromagnetic coil, field shaper and workpiece;

FIG. 3A is a top view of the field shaper shown in FIG. 3;

FIG. 3B is a perspective view, partially in section, of the field shaper and electromagnetic coil shown in FIG. 3;

FIG. 4 is a side elevation, partially in section and partially schematic, of metal forming apparatus, illustrating another embodiment of the invention;

FIG. 4A is a top view of the field shaper shown in FIG. 4;

FIG. 4B is an enlarged fragmentary view, in section, of the field shaper shown in FIG. 4;

FIG. 5 is a side elevation, partially in section and partially schematic, of metal forming apparatus illustrating another embodiment of the invention;

FIG. 5A is a top view of the field shaper shown in FIG. 5;

FIG. 6 is a side elevation, partially in section and partially schematic, of metal forming apparatus illustrating another embodiment of the invention;

FIG. 6A is a top view of a field shaper shown in FIG. 6;

FIG. 6B is an enlarged fragmentary view, in section, of the field shaper shown in FIG. 6;

FIG. 7 is a side elevation, partially in section and partially schematic, of metal forming apparatus illustrating another embodiment of the invention; and

FIG. 7A is a top view of the field shaper shown in FIG. 7.

Referring now to the drawings, and FIG. 1 in particular, there is shown a typical electrical circuit 10 of mag netic forming apparatus, including an electromagnetic coil 12, a source of direct current potential 14, a bank of capacitors 16, and switching means 18. Switching means 18 selectively completes the circuit from the direct current power supply 14 to the bank of capacitors 16, charging the capacitors to a predetermined potential. When it is desired to form the workpiece 13, switching means 16 selectively completes the circuit between capacitors 16 and electromagnetic coil 12, discharging the stored energy in capacitors 16 into electromagnetic coil 12 in the form of a current pulse of predetermined duration. The high intensity magnetic field produced by current flow in the electromagnetic coil 12 induces high currents into workpiece 13, which in turn produces a magnetic field which interacts with the magnetic field of the electromagnetic coil 12, producing mechanical forces on the electromagnetic coil 12 and workpiece 13. The electromagnetic coil 12 is suitably designed and constructed to withstand the mechanical forces to which it is subjected, without damage, While the mechanical forces on the workpiece 13 cause it to be formed or swaged to the desired shape, usually against a suitable die.

In order to concentrate the magnetic field from the electromagnetic coil 12 into the workpiece 13, or utilize one large electromagnetic coil for a variety of workpiece sizes, or in order to direct the magnetic field into desired areas not readily accessible to the electromagnetic coil 12, or a combination of these or other reasons, it is customary to utilize a device called a flux concentrator or field shaper between the electromagnetic coil 12 and the workpiece 13. This is shown in FIGS. 2 and 2A, with the field shaper 20, electromagnetic coil 12, and workpiece 13 being shown in an elevational view, and the electromagnetic coil 12, and field shaper 20 being shown in section. Like reference numerals in FIGS. 1 and 2, and in all of the remaining figures refer to like components.

Power supply 22, shown in FIG. 2 connected in electrical circuit relation with electromagnetic coil 12, represents the source of electrical energy or direct current power supply 14, electrical storage means or capacitors 16, and selective switching means 18, shown in FIG. 1.

Field shaper 20 is designed to have an outside diameter which allows high efiiciency inductive coupling with electromagnetic coil 12, and an internal diameter for receiving workpiece 13. In order to change to different size workpieces 13 it is merely necessary to change to a field shaper having the same outside diameter as shown in FIG. 2, and an inside diameter which would closely couple the intended workpiece. The field shaper 20 is constructed of a conductor of electricity, such as copper, and in order to prevent the field shaper 20 from absorbing all of the energy from the electromagnetic coil 12, it has a radial slot 21, which is shown in FIG. 2, and even more clearly in the top view of the field shaper 20 in FIG. 2A. As illustrated, the radial slot extends parallel with the axis of the field shaper 2t} and electromagnetic coil 12, and is thus parallel with the magnetic flux which is concentrated in the axially extending aperture 24 of the field shaper 20. The field shaper 20 functions as a flux concentrator and director of the magnetic field, as the eddy currents induced into the field shaper 20 act to screen the inside of the field shaper from the magnetic field. Any conductor of electricity placed in a high frequency magnetic field will exclude the magnetic field from all but its outer surfaces. The discharge from the capacitors 16 shown in FIG. 1 is sinusoidal, with the first half cycle occurring in approximately 15-40 microseconds, which establishes a high frequency magnetic field. The magnetic field is forced around the field shaper 20 and into the opening 24 in the field shaper. Thus, the magnetic field is directed and concentrated into the workpiece 13.

With the forming taking place in approximately 20 microseconds, any irregularity or non-uniformity in the magnetic field shows up as an undesired defect in the forming. The slot 21, being parallel with the magnetic field, produces a low reluctance path for the magnetic field, allowing a portion of the magnetic field to leak through the slot. This change in direction of the magnetic field at the slot results in the loss of forming force in this area and may produce an undesirable bump on the surface of the workpiece 13.

This important disadvantage of the prior art field shapes has been overcome by eliminating the radial slot and at the same time absorbing the same, or even less, energy from the electromagnetic field as prior art field shapers. Since a field shaper works upon the principle of magnetic exclusion and not transformer action, it is not essential that the field shaper be a single turn. By making the field shaper multi-turn, and not connecting the start of the initial turn to the end of the final turn, the axial radial slot is completely eliminated, and the field shaper may absorb even less energy than prior art field shapers, as there are no long unbroken paths for energy absorbing circulating currents. The plurality of turns breaks up the paths, and keeps circulating loops to an absolute minimum. Further, the openings between adjacent turns in a multi-turn field shaper are substantially perpendicular to the axis of the field shaper and the electromagnetic coil, and thus substantially perpendicular to the magnetic field. The perpendicular openings between the turns of the field shaper present a very high reluctance to the magnetic field and negligible flux leakage. The field shaper should have at least 2 turns, although more would be preferable. The more turns employed, the more perpendicular the openings between the turns will be to the direction of the flux, resulting in less flux leakage.

FIGS. 3, 3A and 3B illustrate one embodiment of the invention, with'F IG. 3 illustrating an electromagnetic coil 12 formed of an electric conductor shaped to provide a predetermined magnetic field when current flows therethrough, a multi-turn field shaper 30, in section, a workpiece 13, and means for providing a current pulse of predetermined magnitude and time, represented by power supply 22. Field shaper 30 may be formed of coper, aluminum, or any other suitable conductor of electricity, and may be wound on a mandrel, or formed as a hollow cylinder, with an angling saw cut developing the plurality of turns. As illustrated, the turns of field shaper 30 are disposed in side-by-side relationship extending in a longitudinal manner parallel with the axis 38 of the field shaper 30. As =best shown in the perspective view of FIG. 3B, which illustrates the field shaper 30 with the electromagnetic coil 12 in section, the end 32 of the first turn is not connected to the end 34 of the last turn. Thus, the magnetic field is not totally absorbed into the field shaper 30, and serves the same purpose as the axially extending radial slot in prior art field shapers. FIG. 3A shows a top view of the field shaper 30, showing the end 32 of the starting turn.

The multi-turn field shaper functions similarly to the prior art field shaper 20, hereinbefore described. The eddy currents induced into the plurality of turns exclude the magnetic field from all except the outer surface, and forces the magnetic field into the opening 36 in the field shaper 30 and into linkage with the workpiece 13. Since the direction of the magnetic field adjacent to the field shaper 30 is parallel with the axis or center line 38 of the field shaper, it is substantially perpendicular to the openings between the individual turns 40 of the field shaper 30, thus presenting a high reluctance path for the magnetic field and resulting in negligible flux leakage.

FIGS 4, 4A and 4B illustrate another embodiment of the invention, in which the field shaper 50 is similar to the field shaper 30 shown in FIG. 3, except the field shaper is multi-layered as well as having a plurality of longitudinally extending turns. In this instance, two radial layers 51 and 53 are shown. The end 52 of the starting turn and the end 54 of the finishing turn are shown unconnected or floating, which is required for successful operation of the field shaper.

FIG. 4A is a top view of the field shaper 50, and shows the ends 52 and 54 of the starting and finishing turns.

FIG. 4B is a fragmentary view of the field shaper 50, illustrating that a plurality of turns formed by the conductor 56 are electrically insulated from one another by insulation 61, which may be insulating enamel, epoxy, air, or any other suitable electrical insulating means.

FIGS. 5 and 5A illustrate another embodiment of the invention which is similar to the embodiment shown in FIG. 4, except the field shaper 60 is narrowed in the portion adjacent to the workpiece 13. The narrowed portion may be utilized to reach otherwise inaccessible places, or, as shown, may be filled with a strengthening insulating material 62, such as an epoxy impregnated glass tape, to add mechanical strength to the field shaper 60.

The field shaper 60 may be narrowed as shown in FIG. 5, by utilizing a multi-layered field shaper, and using fewer layers of conductor next to the workpiece 13. The .embodiment shown in FIGS. 4 and 5 illustrates how a field shaper may be used to direct the magnetic field into areas which may not be readily accessible to the electromagnetic coil 12, by extending the field shaper into the desired location relative to the workpiece and disposing the electromagnetic coil 12 about a portion of the field shaper that is accessible. An example of where this is desirable is the use of magnetic forming to mount electrical insulating bushings on the covers of electrical transformers, which method and apparatus is described in detail in co-pending application Ser. No. 332,53 8, filed Dec. 23, 1963 by T. E. Franklin, now Patent 3,214,511, which is assigned to the same assignee as the present application.

Instead of forming the multi-turn field shaper of wire type conductor, as shown in the previously described embodiments, the plurality of turns may also be formed by constructing the field shaper of conducting sheet or strip material. This embodiment of the invention is illustrated in FIGS. 6, 6A and 6B. The field shaper 70 may be formed by winding the conducting strip material around a mandrel of predetermined diameter suitable for receiving the intended workpiece, until the desired radial dimensions are obtained for efficient inductive coupling with an electromagnetic coil. The end 72 of the starting turn and the end 74 of the finishing turn are unconnected, as shown in FIG. 6, and even more clearly in the top view of the field shaper 70 shown in FIG. 6A. The turns 71 of the field shaper 70 thus extend radially from the axis 73 of the field shaper 70, and are disposed in nested relationship, with adjacent turns of conducting strip material being electrically insulated from one another by insulation 78, as shown in the fragmentary view of the field shaper 70 in FIG. 6B. The insulation 78 may be in the form of an insulating coating, or a sheet of insulating material may be interleaved with the conducting strip material at the time of winding the field shaper.

FIGS. 7 and 7A are similar to FIGS. 6 and 6A, except FIGS. 7 and 7A illustrate that the conducting, strip material may be of different widths to form a field shaper 80 having the desired shape. For example, as shown in FIG. 7, if it is desired to have a narrow portion on the field shaper, the strip may be started at 82 with a strip of a predetermined width, and when the desired radial buildup has been reached for the narrow portion, the strip may narrow to complete the radial buildup, ending at 84. FIG. 7A is a top view of field shaper 80, which more clearly shows the starting and finishing ends 82 and 84, respectively, of the conducting strip material.

Thus, there has been shown new and improved magnetic metal forming apparatus for forming metals which utilizes a field shaper and produces a uniform magnetic field and a uniform forming action. Further, there has been shown a new and improved field shaper for metal forming apparatus which provides a uniform magnetic field and forming force, and does not possess the axial radial gap of prior art field shapers. Still further, there has been shown a new and improved field shaper for metal forming apparatus which is equal to or superior than prior art field shapers in absorbing a minimum quantity of energy from the magnetic field.

Since numerous changes may be made in the abovedescribed apparatus and difierent embodiments of the invention may be made without departing from the spirit thereof, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative, and not in a limiting sense.

I claim as my invention:

1. Magnetic forming apparatus for forming a metallic workpiece comprising first means for producing a current pulse having a predetermined magnitude and pulse time, an electric conductor shaped to provide a magnetic field having predetermined characteristics when current flows therethrough, second means for selectively connecting said electrical conductor with said first means, field shaping means disposed in inductive relation with said electrical conductor, said field shaping means having at least two continuous helical turns of electrically conductive material defining an aperture therein for receiving the metallic workpiece.

2. Magnetic forming apparatus for forming a metallic workpiece comprising a source of stored electrical energy, an electromagnetic coil, means for selectively connecting said electromagnetic coil in circuit relation with said source of stored electrical energy, and field shaping means disposed and inductive relation with said electromagnetic coil, said field shaping means having at least two continuous helical turns formed of an electrical conductor defining an axially extending aperture for receiving the metallic workpiece.

3. Magnetic forming apparatus for forming a metallic workpiece, comprising first means for storing electrical energy, second means connected in circuit relation with said first means for supplying said first means with electrical energy, an electromagnetic coil, third means for selectively connecting said first means with said electromagnetic coil, field shaping means disposed in inductive relation with said electromagnetic coil, said field shaping means having a plurality of continuous spiral turns formed of an electrically conductive material defining an opening therein for receiving the metallic workpiece.

4. Magentic forming apparatus for forming a metallic workpiece, comprising first means for producing a current pulse having a predetermined magnitude and pulse time, an electrical conductor shaped to provide a magnetic field having predetermined characteristics when current flows therethrough, second means for selectively connecting said electrical conductor With said first means, field shaping means disposed in inductive relation with said electrical conductor, said field shaping means having at least one layer of continuous spiral turns formed of electrically conductive material with said turns forming an opening for receiving the metallic workpiece.

5. Magnetic forming apparatus for forming a metallic workpiece, comprising first means for producing a current pulse having a predetermined magnitude and pulse time, an electrical conductor shaped to proivde a magnetic field having predetermined characteristics when current flows therethrough, second means for selectively connecting said electrical conductor with said first means, field shaping means disposed in inductive relation with said electrical conductor, said field shaping means having a plurality of nested layers of continuous, radially spiralled turns formed from electrically conductive strip material with said plurality of turns electrically insulated from one another and forming an opening for receiving the metallic workpiece.

6. A field shaper for shaping and directing high intensity magnetic fields from an electromagnetic coil into a workpiece, comprising at least two continuous helical turns of electrically conductive material defining an aperture for receiving the workpiece, said turns having a predetermined outside diameter for inductive coupling with the electromagnetic coil.

7. A field shaper for shaping and directing high intensity magnetic fields from an electromagnet'c coil into a workpiece, comprising at least one layer having a plurality of continuous spiral turns of electrically conductive material defining an opening for receiving the workpiece, said plurality of turns having a predetermined outside diameter for inductive coupling with the electromagnetic coil,

8. A field shaper for shaping and directing a high intensity magnetic field from an electromagnetic coil into a workpiece, comprising a plurality of nested, continuous, radially spiralled turns formed from conductive strip material, electrical insulation disposed between said turns, said turns defining an aperture for receiving the workpiece, said turns having a predetermined outside d ameter for inductive coupling with the electromagnetic coil.

References Cited by the Examiner UNITED STATES PATENTS 2,333,015 10/1943 Kramer et a1 336182 2,555,853 6/1951 Irwin 336185 2,976,907 3/1961 Harvey et a1 7256 3,253,443 5/1966 Malmberg 7256 CHARLES W. LANHAM, Primary Examiner.

L. A. LARSON, Assistant Examiner. 

1. MAGNETIC FORMING APPARATUS FOR FORMING A METALLIC WORKPIECE COMPRISING FIRST MEANS FOR PRODUCING A CURRENT PULSE HAVING A PREDETERMINED MAGNITUDE AND PULSE TIME, AN ELECTRIC CONDUCTOR SHAPED TO PROVIDE A MAGNETIC FIELD HAVING PREDETERMINED CHARACTERISTICS WHEN CURRENT FLOWS THERETHROUGH, SECOND MEANS FOR SELECTIVELY CONNECTING SAID ELECTRICAL CONDUCTOR WITH SAID FIRST MEANS, FIELD SHAPING MEANS DISPOSED IN INDUCTIVE RELATION WITH SAID ELECTRICAL CONDUCTOR, SAID FIELD SHAPING MEANS HAVING AT LEAST TWO CONTINUOUS HELICAL TURNS OF ELECTRICALLY CONDUCTIVE MATERIAL DEFINING AN APERTURE THEREIN FOR RECEIVING THE METALLIC WORKPIECE. 